In the pharmaceutical discovery process, high-throughput screening methods and systems have been touted as one method among many, for at least initially identifying promising new pharmaceutical candidate compounds. These methods and systems have been described for use in conjunction with, or even in place of, more traditional rational drug design procedures and methods.
In the past, high-throughput screening operations have simply involved the incorporation of very complex automation elements, e.g., robotics and multiplexed fluid handling systems, in order to carry out assay methods developed for use with conventional technologies, but in massively parallel experiments. Specifically, large numbers of standard assays are carried out in multi-well assay plates into which reagents are dispensed using the automated and highly parallelized fluid handling systems and robotic plate handling equipment. While such systems have increased the number of different materials that can be screened, these systems tend to be extremely complex, relatively unreliable, and have large space, reagent and cost requirements for acquiring and maintaining the overall systems.
Microfluidic devices and systems have been described as potential avenues for performing these high-throughput screening operations while minimizing the space, reagent and cost requirements of the overall systems. However, such systems have largely failed in this respect due to an inability to conveniently introduce large numbers of different reagents into the microfluidic systems. Specifically, such systems have generally relied upon conventional, large, expensive fluid handling systems to introduce samples and reagents into reservoirs on microfluidic devices, effectively xe2x80x98giving backxe2x80x99 any cost or space advantages that would have been realized.
U.S. Pat. No. 5,779,868, and Published International Patent Application Nos. 98/00705 and 98/00231, on the other hand, describe microfluidic devices and systems for use in performing ultra high-throughput screening assays, which devices and systems incorporate an integrated sampling system, or xe2x80x9cworld to chipxe2x80x9d interface, for accessing external materials and delivering them onto the device or LabChip(trademark). These systems typically incorporate a sampling pipettor integrated into the microfluidic system for directly accessing samples, reagents and other materials from sources of such materials, e.g., compound libraries, etc. Integrated pipettor systems have generally proven very effective in rapidly, efficiently and accurately accessing large numbers of different reagents and transporting those reagents into analytical channels.
Despite the effectiveness of these integrated pipettor systems in microfluidic applications, it would generally be desirable to provide such systems with improved structural, interfacing and flow characteristics. The present invention meets these and a variety of other needs.
The present invention provides new and useful improvements to external material sampling or accession systems for microfluidic devices and systems, which provide for improved structural characteristics and improved interfacing.
In a first aspect, the invention provides methods of sampling fluids, e.g., using spontaneous injection. These methods comprise dipping an open end of an open ended fluid-filled capillary element into a source of first fluid, withdrawing the capillary element from the first fluid, and permitting an amount of the first fluid remaining on the open ended capillary to spontaneously inject into the capillary channel. The capillary element is then dipped into a second fluid after a selected time period, where the selected time period is controlled to control the amount of the first fluid permitted to spontaneously inject into the open ended capillary channel.
Another aspect of the invention is a method of introducing a first fluid into a microfluidic device, comprising providing a microfluidic device having a body structure with at least first and second intersecting microscale channels disposed therein, and a capillary element extending from the body structure. The capillary element has first and second ends and a capillary channel disposed through it that is open at the first end, and in fluid communication with at least one of the first and second intersecting microscale channels in the body structure at the second end of the capillary element. The first end of the capillary channel is dipped into a source of the first fluid and then withdrawn, permitting an amount of the first fluid on the first end of the capillary channel to spontaneously inject into the capillary channel. The amount of first fluid injected into the capillary channel is transported into at least one of the first and second microscale channels that are disposed in the body structure.
Another aspect of the invention is a method of reducing or eliminating spontaneous injection. The method comprises dipping a capillary into a source of a first fluid and applying a negative pressure to draw the first fluid into the capillary. The negative pressure is then changed to a positive or negative pressure, thus eliminating the spontaneous injection of the fluid at the tip of the capillary when it is removed from the source of the first fluid. The capillary, which is under a positive or zero pressure, is then optionally dipped into a source of a second fluid. The pressure is changed back to a negative pressure, thus drawing the second fluid into the capillary. The pressure changes are typically made at substrate and enzyme wells as well.
Another aspect of the invention is a method of screening one or more samples. One or more samples are introduced into a microfluidic system and one or more inactivating reagents are added either before a sample, after a sample, or between two samples. The inactivating reagent completely blocks the activity of an enzyme in an enzymatic assay and provides calibration of the percent inhibition level in an assay.
Methods of spatially separating one or more samples in a microfluidic channel are also provided. The method comprises flowing one or more samples through a microscale channel. Spacers are flowed through the channel between the samples to separate one sample from another. The spacers typically comprise a volume of air or an immiscible fluid. The volume of air or immiscible fluid is typically flowed through the microscale channel after each sample or before each sample.
In still another aspect, the present invention provides a microfluidic device that comprises a planar substrate having disposed therein an integrated channel structure that has at least first and second intersecting microscale channels included within. At least the first channel terminates in a substantially rectangular opening in the body structure. The device also includes a capillary element having a capillary channel running through it. At least one end of the capillary element is substantially rectangular. The substantially rectangular end of the capillary element is inserted into the substantially rectangular opening in the body structure and positioned such that the capillary channel in the capillary element is in fluid communication with the at least first microscale channel in the body structure.
The present invention also provides a method of joining a capillary element to a microfluidic device having an integrated channel network. The method comprises providing a microfluidic device having a body structure with at least first and second intersecting microscale channels included within, and having a substantially rectangular opening disposed in the body structure, at least one of the first and second microscale channels terminating in and being in communication with the opening. The method provides a substantially rectangular capillary element having first and second ends and a capillary channel running through the capillary element from the first end to the second end, and wherein the second end has a substantially rectangular shape. The second end of a capillary element is inserted into the opening. The capillary channel in the capillary element is positioned to be in fluid communication with the at least one of the first and second microscale channels that is in communication with the opening.
The present invention also provides a method of joining a capillary element to a microfluidic device incorporating an integrated channel network, which comprises providing first and second substrates, each having at least first planar surfaces. The first planar surface of the first substrate has at least a first microscale groove fabricated therein. Each of the first planar surfaces of the first and second substrates has a first notch fabricated in the first planar surfaces along one edge of the first and second substrates. The first planar surface of the first substrate is mated to the first planar surface of the second substrate whereby the notch in the first substrate corresponds with the notch in the first surface of the second substrate. A first end of a capillary element is inserted into an opening defined by the notch in the first and second substrates. The capillary element has a capillary channel running through the element which is placed in fluid communication with the first microscale groove when the capillary element is inserted into the opening.
Another aspect of the present invention provides a method of introducing a fluid material into a microfluidic device. The microfluidic device is comprised of a body structure which contains an integrated channel network that includes at least first and second intersecting microscale channels. At least the first channel terminates in a substantially rectangular opening in the body structure. The device also includes a capillary element having first and second ends and a capillary channel running through from the first to the second end. The second end of the capillary element is substantially rectangular. The second end of the capillary element is inserted into the substantially rectangular opening in the body structure and positioned such that the capillary channel in the capillary element is in fluid communication with the at least first microscale channel in the body structure. The first end of the capillary element is placed into a source of the fluid material. An amount of the fluid material is then drawn into the capillary channel. The amount of the fluid material is transported through the capillary channel into the at least one of the first and second microscale channels.
A further aspect of the invention is a microfluidic device comprising a body structure having at least first and second channel segments included within. The first and second channel segments each have first and second ends, where the first end of the first channel is in fluid communication with the first end of the second channel at a first fluid junction. The device includes a capillary element attached to and extending from the body structure. The capillary element comprises a capillary channel running through it, which is in fluid communication at one end with the first and second channel segments at the first fluid junction.
Another aspect of the invention is a method of introducing a first fluid material into a microfluidic system, comprising a microfluidic device, which includes a body structure having at least first and second channel segments included within. The first and second channel segments each have first and second ends. The first end of the first channel is in fluid communication with the first end of the second channel at a first fluid junction. The device also includes a capillary element attached to and extending from the body structure. The capillary element includes a capillary channel running through the element, which channel is in fluid communication at one end with the first and second channel segments at the first fluid junction. An amount of the first fluid material is introduced into the capillary channel. The amount of first fluid material is transported through the capillary channel and through the first fluid junction into the first channel segment. A second fluid material is flowed into the first channel segment from the second channel segment during the transporting step.
Another aspect of the invention is a method of transporting materials from a first microscale channel segment to a second microscale channel segment, wherein the first and second channel segments are in fluid communication at a corner having a dead zone. The method includes transporting a discrete volume of material from the first channel segment into the second channel segment around the corner. The fluid flow is simultaneously directed through the dead zone into the second channel segment from a third channel segment that is in fluid communication and collinear with the second channel segment at the corner.
Another aspect of the invention is a microfluidic device comprising a body structure having at least first, second and third channel segments included within. The first, second and third segments are in communication at a first intersection. The second and third channel segments are collinear. The third channel segment has a depth at the intersection that is less than 50% of the depth of the second channel segment.
Another aspect of the invention is a method of transporting material in a microscale channel, comprising introducing a first fluid into the channel that has a first electroosmotic mobility and a first conductivity. A second fluid is introduced into the channel, having a second electroosmotic mobility and a second conductivity. A varying voltage gradient is applied across a length of the channel to maintain a substantially constant average electroosmotic flow rate, despite a change in the total electrical resistance of the channel.
Another aspect of the invention is a microfluidic system, comprising a microfluidic device which includes a microscale channel disposed within it. The microscale channel contains varying volumes of first and second fluids, where the first and second fluids have first and second conductivities, respectively. An electrical controller is operably coupled to the microscale channel for applying a variable electric field across a length of the microscale channel. A computer is operably coupled to the electrical controller, and appropriately programmed to instruct the controller to vary the electric field to maintain a constant average electroosmotic flow rate within the channel, despite a change in total resistance across the length of the channel.